At what point does sex cease to function as a purely practical means of reproduction? In other words, by what process does sex become something more than just a biological imperative; when do things like eroticism and sexuality emerge in an anthropological context?

Sex and sexuality have obviously been well-established cornerstones of humanity's collective social experience for some time, so answering questions like these is understandably difficult. And yet, logic dictates that there was almost certainly a point in time when our ancestors first started to relate to sexuality in ways that differ from the rest of Earth's species. So when might such changes have occurred?

The quick and dirty answer is that exploring the origins of human sexual behavior is not simple. The transition from a strictly animalistic relationship with sex to a human one—a process sometimes referred to as sexual hominization—probably happened a long time ago over the course of a long biological and sociological evolutionary process. Like so many other mysteries rooted in prehistory, it's doubtful that we'll ever know exactly when and how this transformation took place.

Having said that, the tools for understanding the mechanisms of human behavior (including sexuality) in prehistory do exist; make no mistake that there are researchers out there who have poured considerable time and effort into unraveling the secrets of ancient sexual culture. What's more, their findings are beginning to suggest more and more that sexuality most likely emerged during some of humanity's earliest stages of cultural development.

Searching for Sexuality For centuries, researchers have been accumulating collections of archaeological and anthropological discoveries in an ongoing effort to piece together what life might have been like for our ancestors. Among the most enlightening of these finds are those involving prehistoric art work; during the Upper Paleolithic Period (circa 40,000 to 10,000 years ago), our ancestors recorded various aspects of their day-to-day lives in the form of artistic representations, most notably in the form of cave paintings (though engravings on loose stones—not to mention sculptures carved from bones, rocks and horns—have also been recovered). Artistic finds such as these, however, are uncommon. Furthermore, the majority of the paintings, engravings and sculptures that researchers have discovered are of animals. Human representations, by comparison, are relatively scarce.

Enter Spanish researchers Javier Angulo and Marcos García, who since 2003 have devoted thousands of hours to cataloguing depictions of sexuality, reproduction, and eroticism from the Upper Paleolithic, while paying particular attention to prehistoric representations of male genitalia. (Angulo is an MD, PhD in Universidad Europea de Madrid's Department of Urology; García is an anthropologist and expert in Paleolithic archaeology at Universidad del País Vasco).

When I spoke with Angulo and García about their research, they explained that the paucity of Paleolithic art depicting the human form is one of the greatest challenges facing the study of prehistoric sexual behavior. For example, in a review article published in the journal Urology in 2009, the researchers report that in European Paleolithic art, a total of just 702 full-body human representations (as opposed to partial depictions—a handprint, for example) have been discovered since 1864, and that only 74 of these representations can be classified as unambiguously male, sketches of which are shown here.

Fortunately, Angulo and García say that depictions of sexuality in Paleolithic art are not limited to full-body representations. In their most recent publication, for example, the researchers once again pored over descriptions made by scholars of prehistory dating all the way back to 1864, only this time they narrowed their focus down to so-called "portable" specimens, i.e. artifacts that you can hold in your hand.

The researchers write:

Scholars have described at least 60 prehistoric archaeological pieces with a suggestive phallic form in European Paleolithic art from a registry of 462 partial elements...From our perspective 42 of these representations can be considered unequivocal male genital forms.

Interestingly, Angulo and García say that every single one of the 42 "unequivocal male genital forms" (not to mention a little over one third of the 74 full-body male representations described in their 2009 article) are depicted in a state of sexual arousal. More curious still is the observation that 30 of the 42 portable phalli appear to be decorated with a variety of intricate designs, including concentric lines; geometric protrusions; series of carefully arranged dots; and naturalistic forms (including humans and animal figures) — all of which, it bears mentioning, resemble designs found in caves adorned with symbolic, Paleolithic wall art.

Shown here are two examples of the genital ornamentation Angulo and García have observed. These particular phalli have been carved from ivory. The statuette on the left, its shaft bedecked with 6 series of equidistant dots, was recovered from Germany's famous Vogelherd cave. It is estimated to be over 30,000 years old, and is quite possibly the most ancient decorated phallus on record.

The phallus on the right was discovered in the Mas d'Azil cave, located in southwestern France, and is one of the most richly decorated phalli ever recovered. "This phallus, aged approximately 14,000 years, has the anatomical details depicted and is fully decorated," write the researchers. They continue:

Multiple lines of small dots cross the penile glands. Each side of the balanopreputial sulcus is pierced and from these tiny perforations 2 lines, made of multiple marks, descend to the base of the penis. These lines are circumscribed by 8 parallel lines formed by triangles. Other oblique lines cross the body of the penis and coalesce over the urethra.

The designs observed on 30 of the 42 portable phalli, explain the researchers, "probably represent decoration produced by skin scarification, cutting, piercing and tattooing," and could very well "provide a clue to the anthropological origin of current genital tattooing and piercing."

Finding the Present in the Past There are, of course, a number of questions that underly the conclusions drawn by researchers like Angulo and García, chief among them being why? and so what? What do findings like these add to our understanding of prehistoric culture and sexuality? Why is it even important to understand how our ancestors related to sex in the first place?

The study of prehistoric artifacts—even sexual ones—is crucial if we are to understand our ancestors' day-to-day behaviors. The fact that the majority of prehistoric artistic representations are not of humans, for example, but of animals, most probably represents the domination of a zoomorphic mindset in Upper Paleolithic societies. By extension, however, the fact that so many of these human forms feature erect male genitalia suggests that sex and sexuality were likely high on the prehistoric person's list of anthropomorphic considerations. According to Angulo and García:

The interest these beings displayed in both reproduction and sexuality is patent in their works. However, sexuality and procreation were complementary, but differentiated in their mind, because images exist that can be considered highly erotic and not at all of a reproductive character. Most probably, the sexual behavior of Paleolithic humans could have had a wider scope than reproduction itself.

From the Magdalenian period (16,000-10,000 BC) onward, the artistic evidence provide expressive and narrative images of sex as reproduction, pleasure and probably play. Thy undoubtedly reflect a varied sex life. Sensual love and sexual appetite are innate to humanity. It could be said that their sexual practices were, at least since that time, similar to our own.

The authors' explanation hints at another important point of consideration: that for as important as these findings are for our understanding of prehistoric sexual mores, they are equally significant for what they can teach us about our own, modern culture.

When I asked Angulo and García why it is important to understand how our ancestors related to sex and sexuality, they explained that the more we learn about the sexual behavior of our ancestors, the more we understand that today's various sexual attitudes and practices (even genital piercing and tattooing, for example) are—contrary to many social, religious, and/or personal preconceptions—reminiscent of that past.

"Sex is culture," explains García, "not just biology. Sex, for thousands of years, has been about pleasure, play, eroticism."